[openai-dart] Add text to speech APIs

[mirkancal]

Feature request

https://platform.openai.com/docs/guides/text-to-speech

Motivation

Text to speech

Your contribution

Checking but please don't assign yet :D

[davidmigloz]

Thanks @mirkancal !

I need to resolve this issue before being able to add the speech APIs (and the rest of APIs that work files). Once that it's implemented, it should be straightforward to add them.

[decisionslab2]

Thank you, @davidmigloz . Do you have any timeline for when we can expect this feature to be live in the package?